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Inferring fish escape behaviour in trawls based on catch comparison data: model development and evaluation based on
Ludvig Ahm Krag1, Bent Herrmann2, Junita Diana Karlsen1
1DTU Aqua, National Institute of Aquatic Resources, North Sea Science Park, Hirtshals, Denmark.
Plos One
|March 4, 2014
Summary
A new mathematical model analyzes trawl catch data to reveal species- and size-specific fish escape behaviors. This understanding is crucial for designing more selective and sustainable fishing gear.
Area of Science:
- Fisheries Science
- Marine Biology
- Quantitative Ecology
Background:
- Understanding fish behavior is essential for developing efficient and selective fishing gear.
- Direct observation of fish behavior with fishing gear is often limited by harsh underwater conditions.
- Existing methods like optical and acoustic systems face challenges in real-world fishing environments.
Purpose of the Study:
- To develop and apply a novel mathematical model to analyze trawl catch data.
- To extract quantitative information on species- and size-dependent fish escape behavior from towed fishing gear.
- To assess the influence of fish behavior on the selective efficiency of large mesh panels in trawls.
Main Methods:
- Utilized catch comparison data from a twin trawl setup.
- Modified one trawl by replacing a 12 m upper section with 800 mm diamond meshes.
- Applied a mathematical model to quantify length-based escape behavior for cod, haddock, saithe, witch flounder, and lemon sole.
Main Results:
- Quantified escape rates for different species: 85% of saithe, 80% of haddock, 44% of witch flounder, 55% of lemon sole, and 55% of cod (below 68 cm) contacted and escaped the large mesh panel.
- Demonstrated that trawl body selectivity can bias assessments of escape behavior.
- Indirect behavioral assessments using the model aligned with previous direct observation studies.
Conclusions:
- The developed mathematical model provides a viable alternative for studying fish behavior in relation to fishing gear.
- Fish behavior significantly influences the selective efficiency of fishing gear, particularly large mesh panels.
- Accounting for trawl body selectivity is necessary for accurate analysis of escape behavior and gear design.
